Patent Grant
7134946
The present invention generally relates to the field of environmental control for performing cryogenic spray cleaning processes. More specifically, the present invention is directed at cleaning or treating miniature electromechanical device surfaces with cryogenic impingement sprays.
Conventional precision cleaning processes using cryogenic particle impingement sprays, such as solid phase carbon dioxide, require control of the atmosphere containing a treated substrate to prevent the deposition of moisture, particles or other such contaminants onto surfaces during and following cleaning treatments. Environmental control is required because of localized atmospheric perturbations created by the low temperatures and high velocities which are characteristic of these impingement cleaning sprays.
For example, snow particles having a surface temperature of −100 F and traveling through the space between a spray nozzle and a substrate are continuously sublimating in transit and upon impact with the substrate. This rapidly lowers local ambient atmospheric temperature causing contaminants contained therein to condense or “rain-out” of the local atmosphere and onto treated substrate surfaces during or following spray treatments. Moreover, by way of the Bernoulli effect, the cleaning spray stream exhibits lower internal pressure than the surrounding atmosphere which creates venturi currents adjacent to the flow of the stream. These venturi currents cause the local atmosphere surrounding the stream to collapse into the spray stream above the substrate, thus entraining and delivering a mixture of cleaning spray and atmospheric constituents to the substrate. Finally, static charge build-up and accumulation are common to cryogenic sprays due to dielectric and triboelectric characteristics. This presents problems including, for example, potential device damage from electrostatic overstress or electrostatic discharge, and attraction of atmospheric contaminants to treated substrates via electrostatic attractive forces.
Micro-environmental control technology is well established and many techniques have been developed over the years to isolate either a process, a substrate or a worker. The purpose of isolation generally includes protecting workers from toxic chemicals, protecting clean rooms from particles, or protecting delicate processes and substrates from the outside environment.
There are many examples of techniques to control thermal and electrostatic effects during cryogenic impingement sprays using secondary heated or ionized jets or sprays above the substrate surface and delivered either independently or as a component of the cryogenic spray have been used commercially. For example, U.S. Pat. No. 5,409,418 issued to Krone-Schmidt et al. and U.S. Pat. No. 5,354,384 issued to Sneed et al. suggest direct heated or ionized gas impingement techniques and apparatus for heating, purging and deionizing substrate surfaces. The '384 patent suggests the use of a heated gas, such as filtered nitrogen, to provide a pre-heat cycle to a portion of a substrate prior to snow spray cleaning and a post-heat cycle to the substrate following the snow cleaning. This approach relies on “banking heat” into the substrate portion prior to cryogenic spray cleaning by delivering a heated gas stream to a portion of substrate to prevent moisture deposition and adding heat from a heated gas following cryogenic spray treatment. The '384 patent is primarily useful for removing high molecular weight materials such as waxes and adhesive residues having weakened cohesive energy from surfaces by partially melting or softening them prior to spray treatment. However, the approach of the '384 patent does not work well for most substrate treatment applications because many materials being cleaned, or at least portions thereof, have low thermal conductivity, low mass or because highly thermal conductive materials rapidly lose heat to the sublimating snow during impact. This tends to create localized cold spots on even a mostly hot bulk substrate. Examples of such substrates include ceramics, glasses, silicon and other semi-conductor materials, as well as most polymers. Additionally, many electromechanical devices being cleaned are relatively small, providing no appreciable mass for storing heat. Such examples include photodiodes, fiber optic connectors, optical fibers, end-faces, sensors, dies, and CCD's, among many others.
Most significantly, directing a heating spray, or any secondary fluid for that matter, directly at or incident to the substrate surface during and/or following cryogenic cleaning spray treatments causes the entrainment, delivery and deposition of atmospheric contaminants as discussed above. This necessitates housing the cryogenic spray applicator, substrate and secondary gas jets in large, bulky and complex environmental enclosures employing HEPA filtration and dry inert atmospheres, such as included in U.S. Pat. No. 5,315,793, issued to Peterson et al.
In the '418 patent, an apparatus is taught for surrounding the impinging cryogenic spray stream with an ionized inert gas. It is proposed that by surrounding a stream of solid-gas carbon dioxide with a circular stream of ionized gas and applying the two components to the substrate simultaneously controls or eliminates electrostatic discharge at the surface during impingement. However, as also suggested by the '384 patent, the '418 patent suggests secondary stream that entrains, delivers and deposits atmospheric contaminants upon the substrate surfaces being treated. Moreover, contact of the ionizing gas with the stream prior to contact with the surface rapidly eliminates ion concentration and is ineffective in controlling electrostatic dishcarge. Still moreover, using the ionizing spray of the '418 patent independent of the snow spray and which is directed at an angle incident to the surface will further re-contaminate the substrate unless, as taught in the '793 patent, the entire operation is performed in a controlled HEPA filtered chamber.
As devices become smaller and their complexity increases, it is clearly desirable to have a improved processing technique, including a method and apparatus, that enables the use of environmentally safe cleaning agents to remove unwanted organic films and particles. It is desirable to have a technique which prevents additional particles and residues from being deposited on critical surfaces during application of said impingement cleaning sprays. The complete environmental control technique should include all of the basic environmental controls of thermal control, ionization control, and providing a dry and particle free cleaning atmosphere, but not negatively impacting the performance of the impinging cleaning spray. Moreover it would be highly desirable to have a cleaning capability integrated with the aforementioned controlled environment which provides a compact in-line or bench-top critical cleaning solution for manufacturing operations.
The apparatus of the present invention includes a protective enclosure within which is positioned a cryogenic fluid applicator for treating and inspecting a substrate placed therein. The protective enclosure is partially open to the atmosphere and includes a filtered air circulation system and ionization mechanism to provide for a partially-pressurized, heated and ionized re-circulated atmosphere within the protective enclosure to prevent contamination of the substrate. The re-circulated atmosphere flows at a controlled velocity in a manner consistent with the geometry of the cavity and substrate being treated so as not to produce undue turbulence and erratic flow lines within the cavity. The substrate may be held within the cavity by means of a vacuum fixture, operator hands or other suitable fixture. Alternatively, the substrate may be inserted within the partial enclosure, treated and removed using an external robot or conveyed through each side using an automated track.
The present invention further includes a snow generation system connected to the cryogenic fluid applicator. The snow generation system includes a stepped capillary condenser having at least two connected segments of tubing with differing diameters to provide increased Joule-Thompson cooling in the conversion of liquid carbon dioxide to solid carbon dioxide, which reduces clogging and sputtering, improves jetting, and allows for greater spray temperature control. Moreover, the stepped capillary condenser produces coarser particles than a single step capillary.
An apparatus to selectively treat and inspect a substrate is generally indicated 10 in
A re-circulated atmosphere 30, which may be ionized, flows at a controlled velocity in a manner consistent with the geometry of the protective enclosure 12 and substrate 16 being treated so as not to produce undue turbulence and erratic flow lines within the cavity 14. Thus the airflow may be circular, rectangular or any other shape as desired to form the appropriate flow patterns within the open cell cavity 14. Still moreover, the protective enclosure 12 may be designed to be interchangeable to accommodate any number of substrates 16 and substrate geometries, such as reel-to-reel substrates (not shown). The internal cavity 14 is further bounded above and below, respectively, by a regenerated heated clean air outlet plenum 34 positioned within the ceiling 18 and a return air plenum 36 positioned within the base 22 for capturing contaminated air. A regenerated and heated atmosphere 30 is derived by re-circulating air from the perforated return air plenum 36. The regenerated atmosphere 30 is fed through an integrated heater-blower motor 38 and through a filter cartridge 40. The filter cartridge 40 is preferably an ultra low penetration air (ULPA) filter, however, other suitable filters known in the art are well within the scope of the present invention. The regenerated atmosphere 30 flows in a circular motion from the outlet plenum 34, through the cleaning cavity 14, and down through the return plenum 36. Alternatively, various baffles or diffusers (not shown) may be affixed to the outlet plenum 34 to re-direct or diffuse clean air flow over the substrate 16. The apparatus 10 of the present invention further includes an internal point ionizer 42 positioned within cleaning cavity 14 to provide DC, AC or photon ionization 44 to the clean air flow 30. The ionizer 42 is powered by an ionization power supply 46 connected via a power cable 48 to the ionizer 42. The regenerated atmosphere 30 re-circulates between the space comprising above cavity ceiling, along cavity walls, and downward through the return plenum 36 in the base 22 of the protective enclosure 12 resulting in the substrate 16 being contained between the ceiling 18, walls 20, and base 22, protected from ambient atmosphere in a sheath of clean dry ionized atmosphere.
To treat the substrate 16, a carbon dioxide spray treatment nozzle 50 is positioned within the enclosure 12 by means of a bracket 52. The spray treatment nozzle 50 is preferably positioned such that an emitted spray 54 is directed at a suitable angle and distance from the exemplary substrate 16 to perform the snow treatment operations. The spray treatment nozzle 50 is preferably a co-axial nozzle as taught by the present inventor and fully disclosed in U.S. Pat. No. 5,725,154, which is hereby incorporated herein by reference. More preferably, the spray treatment nozzle is a tri-axial type delivering apparatus as taught by the present inventor and fully disclosed in U.S. Provisional Application No. 60/726,466, which is also hereby incorporated herein by reference. It should be noted, though, that any type of nozzle capable of emitting carbon dioxide, in either solid or plasma phases, is well within the scope of the present invention.
A proximity sensor 56 is also positioned within the cavity to detect the presence of the substrate 16 to automatically start or stop the heater-blower motor 38 and ionizer 42. Also connected to the apparatus 10 are a supply of clean-dry-air or CDA 58, a supply of carbon dioxide liquid or gas 60 and a source of electrical power 62. An electronic actuator, such as a footswitch 64, is connected to the apparatus 10 using a suitable electronic control cable 66.
An inspection device 68, including for example a stereo microscope or CCD camera and monitor, is removably affixed to a front panel 70 by means of a mounting bracket 72 to be in visual communication with the spray applicator 50 and substrate 16. Alternatively, the inspection device 68 can be situated using a separate stand (not shown). To aid in the inspection, a light source 78 is connected to the inspection device 68 using a ring light 80. To prevent an operator 84 from introducing human contaminants such as skin or hair into the micro-environment during cleaning and inspection operations, a transparent sneeze guard 86 is included. The operator may be grounded via a wrist strap 88 and grounding element (now shown) through a suitable ground connection plug 90 which provides electrostatic discharge protection for the substrate 16 being treated by the operator 84. Alternatively, the grounding element (not shown) may be connected directly to the exemplary substrate 16 being treated and inspected. For further grounding of the apparatus 10, a common grounding bus is provided internally which is connected to a suitable ground 94.
In operation, the operator 84 positions the substrate 16 within the cleaning cavity 14. Upon so doing, the proximity sensor 56 activates to turn on the heater-blower motor 38 and ionizer 42. The operator 84 then depresses the footswitch 64 to activate a snow generation system 320 or 340, whereby high-velocity snow particles travel from the system via delivery conduit 32 and emit from spray applicator to be directed at the substrate 16 for treatment. Preferably, the snow treatment system 320 or 340 is that as taught by the present inventor and fully disclosed in U.S. application Ser. No. 11/301,442 entitled CARBON DIOXIDE SNOW APPARATUS, filed concurrently with the present application and claiming priority from U.S. Provisional Application No. 60/635,230, both of which are hereby incorporated herein by reference.
The carbon dioxide snow treatment system 320 is generally indicated at 320 in
Being that both embodiments 320 and 340 include similar stepped capillary assemblies 334 and 346, respectively, reference to one shall include reference to the other and all their like parts, for purposes of convenience, unless stated otherwise. Capillary segments 338 are constructed to have increasing, or stepped, diameters in the direction of flow because it has been discovered that by providing stepped capillaries of increasing diameter, certain performance advantages over single capillary diameters are resulted. For instance, when employing carbon dioxide as the dense fluid, larger and harder snow particles can be generated from a relatively smaller feed supply of carbon dioxide. Also, starting with an internal capillary diameter as little about 0.5 mm (0.020 inches) in the first capillary segment, restricted flow into and down the capillary condenser tube is resulted. It has also been discovered that by manipulating the number of steps and incrementally increasing the capillary step diameters, various ranges of solid phase particle size distribution can be produced. Stepped capillary condensation more efficiently condenses the liquid and vapor to solid through sharp near-isobaric expansion cooling while also producing a more desirable range of impact shear stresses.
However, it should be noted that any system for producing carbon dioxide snow is well within the scope of the present invention. The operator 84 can view the treatment process and inspect the substrate 16 either through direct vision or with assistance of the inspection device 68.
A control panel 96 contains all the necessary control valves, pressure regulators, gauges and switches necessary to monitor and control the spray cleaning process. The control panel 96 contains a main power switch 98 which activates the entire system, a spray mode switch 100 which switches spray cleaning operations from continuous spray cleaning mode to stand-by mode or to pulse cleaning mode. The exemplary control panel 96 also contains a carbon dioxide pressure gauge 102 and a CDA or propellant pressure gauge 104. The control panel 96 contains a pulse cycle switch 106 which varies and controls the spray cleaning pulse rate in sub-second pulse increments from 1 to 10 cycles per second or more. A propellant pressure regulator 108 is included to control the carbon dioxide spray pressure from between 0.07 MPa (10 psi) and 1.72 MPa (250 psi) and a carbon dioxide snow metering valve 110 to control carbon dioxide snow flow from zero to about 45 Kg (100 pounds) per hour or more. Finally, the control panel 96 features a digital temperature controller 112 to control the spray propellant temperature between 20 C and 200 C.
Alternatively, and referring to
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
This application claims the benefit U.S. Provisional Patent Application No. 60/635,400 entitled MEHTOD AND APPARATUS FOR SELECTIVELY TREATING AND INSPECTING A SUBSTRATE filed on 13 Dec. 2004 which is hereby incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 60635400 | Dec 2004 | US |
